One of the problems known to be associated with vacuum cleaners is that of noise. It is also perceived that a vacuum cleaner having a higher measure of “airwatts” (which is related to the amount of suction developed by the cleaner at the inlet thereof) will perform better than a vacuum cleaner having a lower measure of airwatts. In relation to the latter, it is well understood that minimising friction losses and pressure drops within the cleaner will result in a maximised measure of airwatts.
The prior art shows that it is known to recover pressure in cyclonic separating apparatus by providing blades or vanes in the outlet thereof such that the spiralling airflow is straightened. See, for example, U.S. Pat. No. 2,771,157. In general, the outlets of cyclonic separating apparatus are normally formed by cylindrical tubes, also known as vortex finders. Outlets which are not cylindrical have occasionally been proposed and U.S. Pat. No. 522,769 illustrates a hexagonal outlet, although no reference is made in the description to the shape of the outlet, nor why the outlet is formed in this way.